Propylene oxide purification



Patented May 1, 1951 f f' UNITED lSTATES PATENT OFFICE PROPYLENE OXIDEPURIFICATION PROCESS Robert L. Mitcheuana William 'r.McNair, Jr.,

Corpus Christi, Tex., assignors to -Celanese Corporation of America, NewYork, N. Y., a corporation of Delaware No Drawing. Application March 1,1950, Serial No. 147,154

. l This invention relates to a purification process for theproductionof purified 1,2-propylene oxide from crude mixtures of organic compoundscontaining 1,2-propylene oxide.

An vobject of this invention is the provision of an improved process forthe separation of purified 1',2-propylene oxide from a crude mixture oforganic compounds comprising essentially 1,2-

prolylene oxide and containing acetaldehyde,

methyl formate, methylal, ethylene oxide and methanol as impurities.

Other objects of this invention will appear from the following detaileddescription. The vapor phase, partial oxidation of aliphatichydrocarbons such as propane or butane, or mixtures thereof, employingair or oxygen as the oxidizing agent, results in the production of acomplex mixture of products including formaldehyde, acetaldehyde,methanol, propionaldehyde, allyl alcohol, isopropyl alcohol, n-propylalcohol, isobutanol, secondary butanol, n-butanol, acetone, methyl ethylketone, methylal, acrolein, tetrahydrofuran, methyl formate and otheres- 6 lClaims. (Cl. 260-348) layers then separated. The upper organiclayer comprises essentially 1,2-propylene oxide While the lower aqueouslayer comprises an aqueous solution of the unreacted alkalinesapom'fying agent ters, formals, acetals and various oxides, as Well iasnumerous other aliphatic compounds, in varying amounts. In order toseparate the complex mixture of oxidation products and to purify each ofthe components so that they will be suitable for commercial use, anintricate products purification scheme is necessary. The purificationinvolves a series of operations yielding a number of crude fractionseach containing a plurality of compounds. One such fraction obtained isa mixture comprising essentially 1,2-propylene oxide and containingacetaldehyde, methyl formate,

,methylaL ethylene oxide and methanol as impurities, The separation of1,2-propylene oxide from this crude mixture by straight distillationmethods is not a practical, commercial step because the relativevolatility of the 1,2-propylene oxide and the methyl formate present inthe crude mixture is near unity. Accordingly, vthe separation of1,2-propylene oxidefrom the mixe ture in highly purified form is notpossible by and alkali formate formed as a product of thesaponil'lcation reaction. The layers may be separated in any convenientmanner and recoveries of 1,2-propylene oxide of over and in a purity of78 to 82% may be readily obtained. The purity of the 1,2-propylene oxidemay be increased to to 99% by a fractional distillation.

In carrying out our novel process, We preferably employ a slightstoichiometric excess of alkaline saponifying agent. An excess ofalkaline saponifying agent of 3 to 20% by weight over that normallyrequired to effect complete saponication of the methyl formate presentis satisfactory. As examples of alkaline saponifying agents Whicliwe mayemploy, there may be mentioned sodium hydroxide, or potassium hydroxide.Preferably, the alkaline saponifying agent is employed in the form of a15 to 25%, say 20%, by Weight aqueous solution.

The strong agitation necessary to effect the 'desired saponificationreaction may be achieved in any convenient manner and high speedmultibladel propeller mixers have been found to be suitable. Optimumresults are obtained, however,

when mixing is effected with the aid of a cen- Vtrifugal pump. The crude1,2-propylene oxide and aqueous saponilying agent are suitablyproportioned by means of ow meters as they are brought together so thatthe desired excess of saponifying agent is thus ensured and the mixtureintroduced into the mixing means employed. Mixing is so effected,thatrthe solutions are subjected to the strong agitation `necessary forcomplete or substantially complete saponication for a period of about 20to 'l'seconds Thus, our process may be carried out continuously byintroducing the crude 1,2-propylene oxide and aqueous saponifyingsolution in suitable proportion into the mixer employed and continuouslyremoving the reaction mixture formed from the. mixer after the desiredsaponication reaction is completed. When employing a centrifugal pump asthe mixing means, the two solutions are fed to the pump in the desiredproportion and, by placing the necessary back pressure on the dischargeside oiV the pump, the solutions being mixed may be maintained therein.for the desired reaction period.

The exothermic reaction which takes place when the aqueous solution ofsaponifyng agent is strongly agitated with the crude 1,2-propylene oxidecontaining the several impurities mentioned causes a rise in thetemperature of the reaction mixture. The crude 1,2-propylene oxide andaqueous saponifying agent are usually mixed with each at a` temperatureof 70 to 100 F. When the exothermic rise in temperature has taken placedue to the saponication reaction which occurs, as well as theresinication of the aldehydes, the temperature of the -nal reactionmixture rises to about 120 to 160 F. The mixture is discharged into asuitable vessel where it separates into layers, the upper layercomprising essentially 1,2-propylene oxide free of. methyl formate andthe lower aqueous layer containing the alkali formate and any unreactedalkaline saponifying agent. The resinied aldehydes present are solidswhich settle at the interface of the two layers. The aqueous layer andresinified aldehydes may be readily separated from the organic layer.

Our process enables 1,2-propylene oxide tol be obtained in a highlypurified form' substantially free of methyl formate, i. e. containingless than 0.02% of methyl formate by Weight.

In order further to illustrate our invention, but without being limitedthereto, the following examples are given:

Example l A crude solution of 1,2-propylene oxide containing, byanalysis, 83.16% by Weight of 1,2*- propylene oxide, 0.69% ofacetaldehyde, 9.71% of methyl formate, 0.26% of ethylene oxide, 4.12%otmethylal and 2.02% of methanol is continuously mixed with an aqueous20% by weight solution of sodium hydroxide in such proportion that a 3%stoichiometric excess of sodium hydroxide is present in the mixture overthat necessary to sa'ponifyv the methyl formate. The mixture is formedata temperature of '78 F. and is then passed through a' centrifugal pumpat such a rate that eachy portion of the solution remains thereinsubject to the resulting strong agitation for about 42 seconds. Thereaction mixture thus formed leaves theY pump at a' temperature of 131F. and is then passed to a decanter Where it separates into two' layers.The upper layer consists ofk 1,2-propyleneoxide con'- taining 0.028%by'weight of methyl formate while the'lower layer comprises an aqueoussolution of unreacted sodium hydroxide, and sodium formate. No1,2-propylene oxide is present in the aqueous layer. The organic layermay be readily decanted from the aqueous layer. The 1,2- propylene oxidethus recovered is 93.2% of that introduced into the system and isobtained in a purity of about 80.5%.

Crude 1,2`propyl'ene oxide of the composition set forth in Example I iscontinuously mixedv with an aqueous 20% by weight solution oA so diumhydroxide in such' proportion that a 17% stoichiometric excess of sodiumhydroxide is present in the resulting mixture over that necessary tosaponify the methyl formate present. The mixture isV formed' at atemperature of. 79 F. and isV then passed to a centrifugal pump' at sucha rate and with sufficient' backpressure that.

each portion of the solution remains therein under strong agitation for50 seconds. Thereaction mixture formed is discharged at a temperatureof'134" F. to a decanterV where'it separates into two layers, the upperlayer'comprising 1-,2-propyleneoxide-containing*0.008% byvweight ofmethyl formate and the lower layer comprising an aqueous solution of thewater-soluble materials. The two layers are then separated. The1,2-propylene oxide is recovered in an amount equal to 91.5 %y of thatintroduced into the system and in a purity of about 79.5%.

, It is to be understood that the foregoing dev i tailed description isgiven merely by way of illustration and that many variations may be madetherein without departing from the spirit of our invention.

Having described our invention, what we desire to secure by'Letters'Patent is:

1. In aVv process for the separation of 1,2- propylene oxide from acrude mixture of 1,2- propylenev oxide containing methyl formate as animpurity, the step which comprises subjecting the crude 1,2-propyleneoxide to strong agitation in admixture with an aqueous solution of analkaline saponifying agent, and then separating the resulting reactionmixture into layers, one layer comprising an aqueous solution of thewatersoluble components and the other comprising 1,2-propylene oxideessentially free of methyl formate.

2. In a process for the separation of 1,2- propylene oxide from a crudemixture of 1,2-

propylene oxide containing methyl formate as any impurity, the stepwhich comprises subjecting the crude 1,2-propylene oxide to strongagitation in admixture with an aqueous solution of an alkalinesaponifying agent in an amount sufcient to provide a stoichiometricexcess of saponifying agent over that necessary to saponify the methylformate present, and then separating the resulting reaction mixture intolayers, one layer comprising an aqueous solution oi the water-solublecomponents and the other comprising 1,2- propylene oxide essentiallyfree of methyl formate.

3. In a processfor the separation of 1,2- propylene oxide from a crudemixture of 1,2- propylene oxide containing methyl formate as animpurity, the step which comprises subjecting the crude 1,2-propyleneoxide to strong agitation in admixture with an aqueous solution of analkaline saponiying agent in an amount suicient to provide a 3 to 20% byweight stoichiometric excess ofsaponifying agent over that necessary tosaponify the methyl formate present, and then separating the resultingreaction mixture into layers, one layer comprising an aqueous'solutionof the water-soluble components and the other comprising 1,2-propyleneoxide essentially free of methyl formate.

4. In a process for the separation of 1,2- propylene oxide from a crudemixture of 1,2- propylene oxide containing methyl'iorrnate as animpurity, the step which comprises subjecting the crude 1,2-p1'opyleneoxide to strong agitation in admixturewith an aqueous solution of sodiumhydroxide in an amount suiiicient to provide a stoichiometric excess ofsodium hydroxide over that necessary to saponify the methyl formatepresent, and then separating the resulting re'- action mixture intolayers, one layer comprising an aqueous solution. of the water-soluble'components and the other comprising 1,2-propylene' oxideess'entially'fre'e oi methyl formate.

5. In a process for the separation' of' 1,2-

propylene oxide from a crude. mixture of 1,2-propyleneoxidecontainingfmethyl formate as an impurity, the stepwhichcomprises subjecting the crude l,2"propylene' oxide to. strong agitationin' f admixture" with an aqueous solution of sodium hydroxide in anamount sufficient to provide a 3 to 20% by Weight stoichiometric excessof sodium hydroxide over that necessary to saponify the methyl formatepresent, and then separating the resulting reaction mixture into layers,one layer comprising an aqueous solution of the water-soluble componentsand theV other comprising 1,2-propylene oxide essentially free of methylformate.

6. In a process for the separation of 1,2- propylene oxide from a crudemixture of 1,2- propylene oxide containing methyl formate as animpurity, the step which comprises subjecting the crude 1,2-propy1eneoxide to strong agitation in admixture with an aqueous solution ofsodium hydroxide in an amount sufficient to provide a 3 to 20% by weightstoichiometric excess of sodium hydroxide over that necessary tosaponify the methyl formate present, maintaining the crude 1,2-propy1eneoxide solution in contact with said aqueous sodium hydroxide under saidstrong agitation for 20 to 75 seconds, and then separating the resultingreaction mixture into layers, one layer comprising an aqueous solutionof the water-soluble components and the other comprising 1,2-propy1eneoxide essentially free of methyl formate.

ROBERT L. MITCHELL. WILLIAM T. MCNAIR,'JR.

No references cited.

1. IN A PROCESS FOR THE SEPARATION OF 1,2PROPYLENE OXIDE FROM A CRUDEMIXTURTE OF 1,2PROPYLENE OXIDE CONTAINING METHYL FORMATE AS AN IMPURITY,THE STEP WHICH COMPRISES SUBJECTING THE CRUDE 1,2-PROPYLENE OXIDE TOSTRONG AGITATION IN ADMIXTURE WITH AN AQUEOUS SOLUTION OF AN ALKALINESAPONIFYING AGENT, AND THEN SEPARATING THE RESULTING REACTION MIXTUREINTO LAYERS ONE LAYER COMPRISING AN AQUEOUS SOLUTION OF THE WATERSOLUBLE COMPONENTS AND THE OTHER COMPRISING 1,2-PROPYLENE OXIDEESSENTIALLY FREE OF METHYL FORMATE.